Numerical solutions of the cubic–quintic NSE by symplectic method with θ = 45.18°, q = 0.01, and different parameter g. Panels (a), (d), and (g) are the phase trajectories; panels (b), (e), and (h) are the time evolutions of A(L/2, t); and panels (c), (f), and (i) are the Fourier spectra of A(L/2, t) corresponding to panels (b), (e), and (h), respectively.